https://about.twitter.com/en-gb/company/display-requirements seems relevant, and I'm not sure that Dreamwidth wants to enable retweet-from-Dreamwidth. I also don't know whether Dreamwidth wants to start having a conversation with Twitter about implementation.
Thoughts upon having looked at the current rules
II.B looks ... interesting ... as well. https://dev.twitter.com/overview/terms/policy#id13
II.C on the profile is more than Dreamwidth does for other connected services, but perhaps it could be in each journal entry: https://dev.twitter.com/overview/terms/policy#id14
https://about.twitter.com/en-gb/company/display-requirements seems relevant, and I'm not sure that Dreamwidth wants to enable retweet-from-Dreamwidth. I also don't know whether Dreamwidth wants to start having a conversation with Twitter about implementation.